1. Field of the Invention
The invention relates to electric circuit connectors. More particularly, the invention relates to connectors having an auto-termination circuit.
2. Description of the Prior Art
The use of special impedance matching circuits for terminating unused output terminals of electric circuits is well known in the art. In high-speed communication networks, for example, it is usually desirable and, in some cases even required by regulating authorities, to have those output terminals that are not connected to other equipment electrically terminated. Terminating devices are generally necessary because networks having non-terminated conductors can be subject to noise. For instance, emissions from various sources of radiation can induce network noise on a pair of non-terminated conductors. Also, a transmission line having non-terminated terminals is subject to noise from signal reflections at these terminals. Further, excessive signal levels on a pair of non-terminated conductors can cause crosstalk to other channels residing in common cabling. As such, it is generally known that a communications network containing non-terminated circuitry can be subject to substantial noise.
A specific example of a circuit within a communication network in which terminating devices are virtually essential is a telephone digital data services (DDS) circuit. Conventional DDS circuits are high-speed private data transmission links that typically propagate signals at digital data rates of 2.4, 4.8, 9.6, 19.2, 38.4, 56.0, or 64.0 kilobits per second. These circuits are most often used by those telephone company customers that require high-speed data links between two or more locations, such as between state lottery machines and a lottery control center, or automatic teller machines (ATM) and an ATM transaction processing center. In the past, telephone companies terminated DDS circuits at a customer's premises with a terminating device called a channel service unit (CSU). A CSU is primarily designed to provide well known digital data interfacing functions such as signal sampling, filtering, regeneration, discrimination and the like. However, besides these digital interfacing functions, such CSU devices are also capable of providing proper electric termination of the DDS circuit at the customer's premises. Additionally, CSU devices provide maintenance loopback functions for use by the telephone company to locate problems and verify proper installation of the end-link facilities.
More recently and primarily motivated by a recent Federal Communications Commission Ruling, CSU devices are no longer installed as telephone equipment but are installed as customer-provided equipment. As such, at initial installation, telephone companies have been using, when deemed necessary, other devices to provide maintenance and termination capabilities. One type of termination device which is currently being installed by telephone companies is called a DDS "smart jack." These devices are capable of providing proper electrical termination of a DDS circuit at the customer's premises as well as maintenance loopback functions. Maintenance loopback functions enable a telephone company to remotely disconnect the customer's equipment and loopback any transmitted signal to the central office. In this manner, the telephone company can test the transmission circuit to/from the DDS "smart jack". In addition, most DDS "smart jacks" provide a repeater function which permits extended-range operation. In other words, the DDS "smart jack" permits the telephone company to provide DDS over longer loops than could have been possible without the DDS "smart jack". A repeater is usually required when a DDS loop is of a length that attenuates a signal propagating thereupon by between 34 dB and 45 dB.
Though the "smart jack" and similar terminating devices have been successfully used, they have not been widely accepted in all situations for a number of reasons. For one, "smart jacks" are relatively expensive. Also, most "smart jacks" are active devices which must be connected to the customer's power. This power requirement can present several problems. First, a customer may not wish to have an additional equipment (a "smart jack") connected to the customer's power supply, especially if those functions that require power, e.g., the repeater functions, are not needed by the customer. Also, at the time that many DDS installations are provided, i.e., during building construction, the customer is typically not ready to connect its equipment to a power supply and/or the customer's power is not yet turned on. As such, in many DDS installations, use of the "smart jack" or other active electric termination is not possible, leaving the telephone company with the problem of not being able to verify proper installation. Also, as mentioned above, a non-terminated DDS installation produces an open loop within the communications network which can be a source of substantial network noise. It is noted, of course, that the foregoing problems are not limited to communication networks, but can also occur in other high-speed electronic systems.
Consequently, those concerned with the development of connectors for DDS circuits and other systems requiring electrical termination have long recognized the need for improved circuits that can provide auto-termination and maintenance functions in a simple, reliable and inexpensive device.